Bitter about adult's teasing (7)
I believe the answer is:
baiting
'teasing' is the definition.
('bait' can be a synonym of 'tease')
'bitter about adult's' is the wordplay.
I cannot really understand how this works, but
'about' could be 'a' (abbreviation in Chambers) and 'a' is located in the answer.
'bitter' could be 'biting' (synonyms) and 'biting' is located in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for baiting that I've seen is " Taunting".)